This invention relates to a contact converting structure of a semiconductor wafer.
A semiconductor wafer comprises a plurality of semiconductor chips, and most of the semiconductor chips have groups of electrodes arranged in array along four or two sides of a lower surface thereof. Recently, it became customary for a group of electrodes to be uniformly arranged over an entire surface on the lower side of the semiconductor chip.
In case the arranged pitches of the semiconductor chips are very small, a need occurs to convert such pitches in order to correspond to the pitches of electrode connecting pads on a wiring circuit board on which the semiconductor chip is to be placed.
In addition, there is a further need for conversion to a ball-shaped contact structure or the like, which is suited for connection with an electrode connecting pad of a wiring circuit board.
A conventional technique aimed at packaging at a wafer level is shown, for example, in FIG. 1. In this conventional technique, a polyimide substrate 1 having a number of ball type contacts 2 comprised of solder balls are separately formed from a semiconductor wafer 3. The ball type contacts 2 of each polyimide substrate 1 are bonded to electrodes 5 of the semiconductor wafer through leads 6. Between the polyimide substrate 1 and the semiconductor wafer 3, a rubber-containing elastic resin is charged to form an elastic resin layer 4. The leads 6 and connecting portions at opposite ends thereof are embedded in the elastic resin layer 4, and thereafter, semiconductor chips are divided from the semiconductor wafer.
The above prior art makes it possible to convert the pitches and configuration of the electrodes of the semiconductor chips. In this art, it is necessary that the semiconductor wafer 3 and the polyimide substrate 1 are connected through the leads 6, the elastic resin is charged between the wafer 3 and the substrate 1, the elastic resin layer 4 is formed by charging the elastic resin between the wafer 3 and the substrate 1, and the ball type contacts 2 are formed. However, technical difficulties are encountered when carrying out a connecting operation in a very small space between the semiconductor wafer 3 and the polyimide substrate 1 through the leads 6. Although the above proposal for performing an interlayer connection through the leads 6 at the wafer level and charging the elastic resin between the wafer and the substrate is a remarkable technique for receiving attention in the respect that the packaging, the pitch conversion and the configuration conversion are intended at the wafer level, and in the respect that there is a provision of a stress easing mechanism caused by differences in thermal expansion, there still remain various problems in manufacturing technique and cost.
The typical problem involved in the above prior art resides in moisture absorbability of silicon rubber and polyimide commonly used with the above rubber-based elastic resin layer 4, elastic resin, for example.
Since a semiconductor chip obtained by dividing the wafer has the cut-out surfaces of the elastic resin layer 4 (silicon rubber, etc.) and the polyimide substrate 1 exposed or nearly exposed to the side surface, moisture tends to permeate into the elastic resin and the polyimide through the cut-out surfaces to cause adverse effects at the leads and their connecting areas, thus resulting in decreased reliability.
Moreover, since the above prior art is directed to a manufacturing process in which the polyimide substrate 1 having the ball type contacts 2 and the semiconductor wafer 3 are manufactured separately, an interlayer connection is performed in a very small gap between the substrate 1 and the wafer 3, and elastic resin is charged therebetween, the cost becomes high and in addition, the above-mentioned technical difficulties for manufacture are involved.